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Beta Diversity (beta + diversity)
Selected AbstractsSpatial scale and the diversity of macroinvertebrates in a Neotropical catchmentFRESHWATER BIOLOGY, Issue 2 2010RAPHAEL LIGEIRO Summary 1.,Lotic ecosystems can be studied on several spatial scales, and usually show high heterogeneity at all of them in terms of biological and environmental characteristics. Understanding and predicting the taxonomic composition of biological communities is challenging and compounded by the problem of scale. Additive diversity partitioning is a tool that can show the diversity that occurs at different scales. 2.,We evaluated the spatial distribution of benthic macroinvertebrates in a tropical headwater catchment (S.E. Brazil) during the dry season and compared alpha and beta diversities at the scales of stream segments, reaches, riffles and microhabitats (substratum types: gravels, stones and leaf litter). We used family richness as our estimate of diversity. Sampling was hierarchical, and included three stream segments, two stream reaches per segment, three riffles per reach, three microhabitats per riffle and three Surber sample units per microhabitat. 3.,Classification analysis of the 53 families found revealed groups formed in terms of stream segment and microhabitat, but not in terms of stream reaches and riffles. Separate partition analyses for each microhabitat showed that litter supported lower alpha diversity (28%) than did stones (36%) or gravel (42%). In all cases, alpha diversity at the microhabitat scale was lower than expected under a null model that assumed no aggregation of the fauna. 4.,Beta diversity among patches of the microhabitats in riffles depended on substratum type. It was lower than expected in litter, similar in stone and higher in gravel. Beta diversities among riffles and among reaches were as expected under the null model. On the other hand, beta diversity observed was higher than expected at the scale of stream segments for all microhabitat types. 5., We conclude that efficient diversity inventories should concentrate sampling in different microhabitats and stream sites. In the present study, sampling restricted to stream segments and substratum types (i.e. excluding riffles and stream reaches) would produce around 75% of all observed families using 17% of the sampling effort employed. This finding indicates that intensive sampling (many riffles and reaches) in few stream segments does not result in efficient assessment of diversity in a region. [source] A latitudinal gradient of beta diversity for exotic vascular plant species in North AmericaDIVERSITY AND DISTRIBUTIONS, Issue 3 2008Hong Qian ABSTRACT Determining relationships between the ranges of introduced species and geographical and environmental factors is an important step in understanding the mechanisms and processes of the spread of introduced species. In this study, I examined the beta diversity and latitude relationship for all naturalized exotic species of vascular plants in North America at a continental scale. Beta diversity was calculated as the absolute value of the slope of the relationship between the natural logarithm of the Simpson index of similarity (lnS) and spatial distance between pairs of state-level exotic floras within four latitudinal zones examined. Relative contributions of spatial distance and environmental difference to species turnover between exotic floras were examined. I found that beta diversity decreased monotonically from low to high latitudes: beta diversity for the southernmost zone was shallower than that for the northernmost zone by a factor of 2.6. Regression models of lnS in relation to spatial distance and environmental (climatic and topographical) difference for each latitudinal zone demonstrated that the explanatory power of these variables diminishes monotonically with latitude: the explained variance in lnS is 70.4%, 62.1%, 53.9%, and 33.9%, respectively, for the four latitudinal zones from south to north. For the southernmost zone, 58.3% of the variance in lnS is explained by climate variables and topography, and spatial distance explains only 2.3% of the variance. In contrast, for the northernmost zone, more than half the amount (22.5%) of the explained variance in lnS is attributable to spatial distance, and the remaining (18.9%) of the explained variance is attributable to climate variables and topography. [source] Beta diversity of geometrid moths (Lepidoptera: Geometridae) in an Andean montane rainforestDIVERSITY AND DISTRIBUTIONS, Issue 5 2003Gunnar Brehm Abstract. Turnover in species composition of the extremely species-rich family Geometridae (Lepidoptera) was investigated along an elevational gradient ranging from 1040 m to 2677 m above sea level. Moths were sampled using weak light traps (30 W) in three field periods in 1999 and 2000 in an Andean montane rainforest in the province of Zamora-Chinchipe in southern Ecuador. A total of 13 938 specimens representing 1010 species were analysed. Similarities of ensembles of all geometrid moths and of the subfamilies Ennominae and Larentiinae were calculated using the NESS index (with mmax). Ordinations performed using nonmetric multidimensional scaling (NMDS) and correspondence analysis depicted a gradual change of the ensembles along the altitudinal gradient. Extracted ordination scores significantly correlate with altitude (,0.97 , r , ,0.95, P < 0.001) and with ambient air temperature (0.93 , r , 0.97, P < 0.001). Temperature is therefore assumed to be the most important abiotic determinant responsible for the species turnover among the moths. Matrix correlation tests were performed in order to compare faunal matrices with matrices derived from available environmental factors. Both tree diversity and vegetation structure significantly correlate with faunal data, but tree diversity explains considerably more of the data variability (range: Mantel r = 0.81,0.83, P < 0.001) than vegetation structure (range: Mantel r = 0.35, P < 0.005 to r = 0.43, P < 0.001). Tree diversity also changes gradually and scores of the first NMDS dimension are highly significantly correlated with altitude (r = 0.98, P < 0.001). A common underlying factor such as ambient temperature might also be responsible for such vegetation changes. Additionally, simulated model data was developed that assumed a constant turnover of moth species and equal elevational ranges of all species involved. Despite the simplicity of the models, they fit empirical data very well (Mantel r > 0.80 and P < 0.001 in all models). [source] Beta diversity: synthesis and a guide for the perplexedECOGRAPHY, Issue 1 2010Robert K. Colwell No abstract is available for this article. [source] Beta diversity and latitude in North American mammals: testing the hypothesis of covariationECOGRAPHY, Issue 5 2004Pilar Rodríguez Several hypotheses attempt to explain the latitudinal gradient of species diversity, but some basic aspects of the pattern remain insufficiently explored, including the effect of scales and the role of beta diversity. To explore such components of the latitudinal gradient, we tested the hypothesis of covariation, which states that the gradient of species diversity should show the same pattern regardless of the scale of analysis. The hypothesis implies that there should be no gradients of beta diversity, of regional range size within regions, and of the slope of the species-area curve. For the fauna of North American mammals, we found contrasting results for bats and non-volant species. We could reject the hypothesis of covariation for non-volant mammals, for which the number of species increases towards lower latitudes, but at different rates depending on the scale. Also, for this group, beta diversity is higher at lower latitudes, the regional range size within regions is smaller at lower latitudes, and z, the slope of the species-area relationship is higher at lower latitudes. Contrarily bats did not show significant deviations from the predictions of the hypothesis of covariation: at two different scales, species richness shows similar trends of increase at lower latitudes, and no gradient can be demonstrated for beta diversity, for regional range size, or for the slopes of the species-area curve. Our results show that the higher diversity of non-volant mammals in tropical areas of North America is a consequence of the increase in beta diversity and not of higher diversity at smaller scales. In contrast, the diversity of bats at both scales is higher at lower latitudes. These contrasting patterns suggest different causes for the latitudinal gradient of species diversity in the two groups that are ultimately determined by differences in the patterns of geographic distribution of the species. [source] Spatial scale and the diversity of macroinvertebrates in a Neotropical catchmentFRESHWATER BIOLOGY, Issue 2 2010RAPHAEL LIGEIRO Summary 1.,Lotic ecosystems can be studied on several spatial scales, and usually show high heterogeneity at all of them in terms of biological and environmental characteristics. Understanding and predicting the taxonomic composition of biological communities is challenging and compounded by the problem of scale. Additive diversity partitioning is a tool that can show the diversity that occurs at different scales. 2.,We evaluated the spatial distribution of benthic macroinvertebrates in a tropical headwater catchment (S.E. Brazil) during the dry season and compared alpha and beta diversities at the scales of stream segments, reaches, riffles and microhabitats (substratum types: gravels, stones and leaf litter). We used family richness as our estimate of diversity. Sampling was hierarchical, and included three stream segments, two stream reaches per segment, three riffles per reach, three microhabitats per riffle and three Surber sample units per microhabitat. 3.,Classification analysis of the 53 families found revealed groups formed in terms of stream segment and microhabitat, but not in terms of stream reaches and riffles. Separate partition analyses for each microhabitat showed that litter supported lower alpha diversity (28%) than did stones (36%) or gravel (42%). In all cases, alpha diversity at the microhabitat scale was lower than expected under a null model that assumed no aggregation of the fauna. 4.,Beta diversity among patches of the microhabitats in riffles depended on substratum type. It was lower than expected in litter, similar in stone and higher in gravel. Beta diversities among riffles and among reaches were as expected under the null model. On the other hand, beta diversity observed was higher than expected at the scale of stream segments for all microhabitat types. 5., We conclude that efficient diversity inventories should concentrate sampling in different microhabitats and stream sites. In the present study, sampling restricted to stream segments and substratum types (i.e. excluding riffles and stream reaches) would produce around 75% of all observed families using 17% of the sampling effort employed. This finding indicates that intensive sampling (many riffles and reaches) in few stream segments does not result in efficient assessment of diversity in a region. [source] The latitudinal gradient of beta diversity in relation to climate and topography for mammals in North AmericaGLOBAL ECOLOGY, Issue 1 2009Hong Qian ABSTRACT Aim Spatial turnover of species, or beta diversity, varies in relation to geographical distance and environmental conditions, as well as spatial scale. We evaluated the explanatory power of distance, climate and topography on beta diversity of mammalian faunas of North America in relation to latitude. Location North America north of Mexico. Methods The study area was divided into 313 equal-area quadrats (241 × 241 km). Faunal data for all continental mammals were compiled for these quadrats, which were divided among five latitudinal zones. These zones were comparable in terms of latitudinal and longitudinal span, climatic gradients and elevational gradients. We used the natural logarithm of the Jaccard index (lnJ) to measure species turnover between pairs of quadrats within each latitudinal zone. The slope of lnJ in relation to distance was compared among latitudinal zones. We used partial regression to partition the variance in lnJ into the components uniquely explained by distance and by environmental differences, as well as jointly by distance and environmental differences. Results Mammalian faunas of North America differ more from each other at lower latitudes than at higher latitudes. Regression models of lnJ in relation to distance, climatic difference and topographic difference for each zone demonstrated that these variables have high explanatory power that diminishes with latitude. Beta diversity is higher for zones with higher mean annual temperature, lower seasonality of temperature and greater topographic complexity. For each latitudinal zone, distance and environmental differences explain a greater proportion of the variance in lnJ than distance, climate or topography does separately. Main conclusions The latitudinal gradient in beta diversity of North American mammals corresponds to a macroclimatic gradient of decreasing mean annual temperature and increasing seasonality of temperature from south to north. Most of the variance in spatial turnover is explained by distance and environmental differences jointly rather than distance, climate or topography separately. The high predictive power of geographical distance, climatic conditions and topography on spatial turnover could result from the direct effects of physical limiting factors or from ecological and evolutionary processes that are also influenced by the geographical template. [source] Beta diversity of plant,insect food webs in tropical forests: a conceptual frameworkINSECT CONSERVATION AND DIVERSITY, Issue 1 2009VOJTECH NOVOTNY Abstract., 1Beta diversity of plant,herbivore food webs, defined as turnover of trophic interactions between the food webs, represents a potentially useful extension of traditional studies of plant and herbivore beta diversity as it integrates spatial turnover of plant and herbivore species with changes in herbivore host plant preferences. 2Beta diversity of plant,herbivore food webs can be partitioned into four components, corresponding to the turnover of plant,herbivore interactions due to change in (i) both plant and herbivore species, (ii) plant, but not herbivore, species, (iii) herbivore, but not plant, species, and (iv) herbivore host preferences between food webs. These components can be quantified using a range of existing beta diversity indices. 3Relative magnitude of plant and herbivore beta diversity of plant,herbivore food webs can be analysed as an outcome of herbivore (i) host specificity, (ii) ability to track host plant populations by dispersal, and (iii) response to environmental conditions, competitors and enemies. The relative importance of these factors in tropical ecosystems remains to be determined. [source] Spatial patterns of benthic diversity: is there a latitudinal gradient along the Norwegian continental shelf?JOURNAL OF ANIMAL ECOLOGY, Issue 3 2002Karie. Summary 1We examined data on soft-sediment macrobenthos (organisms retained on a 1-mm sieve) from a transect of c. 1960 km along the Norwegian continental shelf (56,71°N), covering a range of water depths (65,434 m) and varying sediment properties. 2A total of 809 species was recorded from 101 sites. Of these, 36% were restricted to one or two sites, and 29% were represented by one or two individuals. No species spanned the entire transect. Polychaetes were the dominant taxonomic group, followed by crustaceans, molluscs and echinoderms. 3Alpha diversity (sample species richness) was highly variable (35,148 species) but showed no evidence of a relationship to latitude or other environmental variables. 4Beta diversity was measured as Whittaker's ,W, the number of shared species, complementarity (biotic distinctness) and Bray,Curtis similarity, and there was no evidence of a latitudinal trend on the shelf. Beta diversity increased with the level of environmental variability, and was highest in the southern-central area, followed by the most northern area. Change in environmental variables had a stronger effect on beta diversity than spatial distance between sites. 5Gamma diversity was computed by pooling samples over large areas. There was no convincing evidence of a latitudinal cline in gamma diversity, but gamma diversity increased with the level of environmental heterogeneity. Mean alpha diversity and gamma diversity were not significantly correlated. Whereas mean complementarity and mean Bray,Curtis similarity were related to gamma diversity, ,W was not. [source] Beta diversity of frogs in the forests of New Guinea, Amazonia and Europe: contrasting tropical and temperate communitiesJOURNAL OF BIOGEOGRAPHY, Issue 5 2009Chris Dahl Abstract Aim, To test the hypothesis that animal communities within environmentally relatively uniform lowland forests are characterized by low beta diversity, both in tropical and in temperate areas. Location, Lowland forests in the basins of the Sepik and Ramu rivers in New Guinea, the Amazon river in Bolivia, and the Elbe and Dyje rivers in the Czech Republic. Methods, A network of 5,6 study sites spanning distances from 20,80 to 300,500 km in each study area was systematically surveyed for all frogs, using visual detection and call tracking. The community data were analysed for alpha and beta diversity. Results, Local (alpha) diversity of frog communities was similar in the two tropical areas, New Guinea (mean ± SE of 22 ± 1.4 species per site) and Amazonia (24 ± 1.7 species), but was significantly lower in Europe (8 ± 0.8 species). In Amazonia, 36 of the total of 70 species were recorded from single sites. In contrast, widespread species dominated in Europe, whereas New Guinea exhibited an intermediate pattern with both local and widespread species well represented. The rate of species accumulation across different sites was lowest in Europe, intermediate in New Guinea and highest in Amazonia. The regional species diversity, expressed as the combined number of species from five study sites, was 1.5 times higher than the local species diversity at a single site in Europe, 2.0 times higher in New Guinea and 2.7 times higher in Amazonia. The proportion of species shared between communities decreased with geographic distance in New Guinea and Europe, but not in Amazonia. Main conclusions, Frog communities in the lowland tropical rain forests of New Guinea and Amazonia had similar numbers of species, but differed in their beta diversity. More species in Amazonia had restricted distributions than in New Guinea. Both tropical areas had markedly higher alpha and beta diversity than the temperate area in Europe. [source] Mapping continuous fields of forest alpha and beta diversityAPPLIED VEGETATION SCIENCE, Issue 4 2009Hannes Feilhauer Abstract Question: How to map continuous fields of forest alpha and beta diversity in remote areas, based on easily accessible spatial data. Location: Kyrgyzstan/Central Asia. Methods: The study relied on a combination of predictive mapping and remote sensing. Punctual measurements of alpha diversity were linked to topography and reflectance using regression models. For beta diversity, ordination techniques were employed to extract major vegetation gradients. Scores on the ordination axes were regressed against topography as well as reflectance and subsequently mapped. Beta diversity was mapped as spatial turnover rate along these axes. Results: The diversity maps quantified species counts and turnover in a spatially contiguous manner while taking into account fuzzy transitions. The variance explained by regression models ranged from 51% to 61% in cross-validation. Many of the observed differences were caused by differences in species shares. The occurrence of walnut, in particular, showed a negative relation to woody species numbers. Conclusion: Mapping biodiversity in remote areas can be based on easily accessible spatial data in combination with a set of calibration field samples. With regard to human influence on walnut dominance, a total removal of human land use would be counterproductive in terms of diversity conservation. The results of this study highlight the need for comprehensive analyses of diversity patterns that include spatially contiguous quantifications of species numbers, shares and turnover rates. [source] A diversity of beta diversities: straightening up a concept gone awry.ECOGRAPHY, Issue 1 2010Part 1. The term beta diversity has been used to refer to a wide variety of phenomena. Although all of these encompass some kind of compositional heterogeneity between places, many are not related to each other in any predictable way. The present two-part review aims to put the different phenomena that have been called a beta component of diversity into a common conceptual framework, and to explain what each of them measures. In this first part, the focus is on defining beta diversity. This involves deciding what diversity is and how the observed total or gamma diversity (,) is partitioned into alpha (,) and beta (,) components. Several different definitions of "beta diversity" that result from these decisions have been used in the ecological literature. True beta diversity is obtained when the total effective number of species in a dataset (true gamma diversity,) is multiplicatively partitioned into the effective number of species per compositionally distinct virtual sampling unit (true alpha diversity,d) and the effective number of such compositional units (,Md=,/,d). All true diversities quantify the effective number of types of entities. Because the other variants of "beta diversity" that have been used by ecologists quantify other phenomena, an alternative nomenclature is proposed here for the seven most popular beta components: regional-to-local diversity ratio, two-way diversity ratio, absolute effective species turnover (=regional diversity excess), Whittaker's effective species turnover, proportional effective species turnover, regional entropy excess and regional variance excess. In the second part of the review, the focus will be on how to quantify these phenomena in practice. This involves deciding how the sampling units that contribute to total diversity are selected, and whether the entity that is quantified is all of "beta diversity", a specific part of "beta diversity", the rate of change in "beta diversity" in relation to a given external factor, or something else. [source] Spatial scale and the diversity of macroinvertebrates in a Neotropical catchmentFRESHWATER BIOLOGY, Issue 2 2010RAPHAEL LIGEIRO Summary 1.,Lotic ecosystems can be studied on several spatial scales, and usually show high heterogeneity at all of them in terms of biological and environmental characteristics. Understanding and predicting the taxonomic composition of biological communities is challenging and compounded by the problem of scale. Additive diversity partitioning is a tool that can show the diversity that occurs at different scales. 2.,We evaluated the spatial distribution of benthic macroinvertebrates in a tropical headwater catchment (S.E. Brazil) during the dry season and compared alpha and beta diversities at the scales of stream segments, reaches, riffles and microhabitats (substratum types: gravels, stones and leaf litter). We used family richness as our estimate of diversity. Sampling was hierarchical, and included three stream segments, two stream reaches per segment, three riffles per reach, three microhabitats per riffle and three Surber sample units per microhabitat. 3.,Classification analysis of the 53 families found revealed groups formed in terms of stream segment and microhabitat, but not in terms of stream reaches and riffles. Separate partition analyses for each microhabitat showed that litter supported lower alpha diversity (28%) than did stones (36%) or gravel (42%). In all cases, alpha diversity at the microhabitat scale was lower than expected under a null model that assumed no aggregation of the fauna. 4.,Beta diversity among patches of the microhabitats in riffles depended on substratum type. It was lower than expected in litter, similar in stone and higher in gravel. Beta diversities among riffles and among reaches were as expected under the null model. On the other hand, beta diversity observed was higher than expected at the scale of stream segments for all microhabitat types. 5., We conclude that efficient diversity inventories should concentrate sampling in different microhabitats and stream sites. In the present study, sampling restricted to stream segments and substratum types (i.e. excluding riffles and stream reaches) would produce around 75% of all observed families using 17% of the sampling effort employed. This finding indicates that intensive sampling (many riffles and reaches) in few stream segments does not result in efficient assessment of diversity in a region. [source] Priority Wetland Invertebrates as Conservation SurrogatesCONSERVATION BIOLOGY, Issue 2 2010S. J. ORMEROD agua dulce; caracoles; conservación; especies paraguas; especies sustitutas; gasterópodos Abstract:,Invertebrates are important functionally in most ecosystems, but seldom appraised as surrogate indicators of biological diversity. Priority species might be good candidates; thus, here we evaluated whether three freshwater invertebrates listed in the U.K. Biodiversity Action Plan indicated the richness, composition, and conservation importance of associated wetland organisms as defined respectively by their alpha diversity, beta diversity, and threat status. Sites occupied by each of the gastropods Segmentina nitida, Anisus vorticulus, and Valvata macrostoma had greater species richness of gastropods and greater conservation importance than other sites. Each also characterized species assemblages associated with significant variations between locations in alpha or beta diversity among other mollusks and aquatic macrophytes. Because of their distinct resource requirements, conserving the three priority species extended the range of wetland types under management for nature conservation by 18% and the associated gastropod niche-space by around 33%. Although nonpriority species indicated variations in richness, composition, and conservation importance among other organisms as effectively as priority species, none characterized such a wide range of high-quality wetland types. We conclude that priority invertebrates are no more effective than nonpriority species as indicators of alpha and beta diversity or conservation importance among associated organisms. Nevertheless, conserving priority species can extend the array of distinct environments that are protected for their specialized biodiversity and environmental quality. We suggest that this is a key role for priority species and conservation surrogates more generally, and, on our evidence, can best be delivered through multiple species with contrasting habitat requirements. Resumen:,Los invertebrados son funcionalmente importantes en la mayoría de los ecosistemas, pero raramente son valorados como indicadores sustitutos de la diversidad biológica. Las especies prioritarias pueden ser buenos candidatos; por lo tanto, aquí evaluamos sí tres especies de invertebrados enlistados en el Plan de Acción para la Biodiversidad del Reino Unido eran indicadores de la riqueza, la composición e importancia para la conservación de organismos de humedal asociados definida por su diversidad alfa, diversidad beta y estatus de amenaza respectivamente. Los sitios ocupados por cada uno de los gasterópodos Segmentina nitida, Anisus vorticulus and Valvata macrostoma tuvieron una mucho mayor riqueza de gasterópodos y mayor importancia para la conservación que otros sitios. Cada uno también caracterizó a los ensambles asociados con variaciones significativas entre localidades en la diversidad alfa o entre otros moluscos y macrofitas acuáticas en la diversidad beta. Debido a sus diferentes requerimientos de recursos, la conservación de las tres especies prioritarias se amplió la extensión de todos los tipos de humedal bajo manejo para la conservación de la naturaleza en 18% y el nicho-espacio de los gasterópodos asociados se amplió alrededor de 33%. Aunque las especies no prioritarias indicaron variaciones en riqueza, composición e importancia de conservación entre otros organismos tan efectivamente como las especies prioritarias, ninguna caracterizó un rango tan amplio de humedales de alta calidad. Concluimos que los invertebrados prioritarios no son más efectivos que las especies no prioritarias como indicadores de la diversidad alfa y beta ni de la importancia para la conservación entre organismos asociados. Sin embargo, la conservación de especies prioritarias puede ampliar el conjunto de ambientes diferentes que son protegidos por su biodiversidad especializada y calidad ambiental. Sugerimos que este es un papel clave para las especies prioritarias y, más generalmente, para los sustitutos de conservación, y, con base en nuestra evidencia, puede ser desarrollado mediante múltiples especies con requerimientos de hábitat contrastantes. [source] Biogeographic Crossroads as Priority Areas for Biodiversity ConservationCONSERVATION BIOLOGY, Issue 6 2002Sacha Spector I suggest that targeting the regions where biogeographic assemblages intersect,"biogeographic crossroads",is a strategy that may achieve significant conservation economy by focusing on areas that satisfy many conservation criteria. I used a combination of data on Scarabaeine beetles in Bolivia and on other taxa and locations from the literature to consider the short- and long-term benefits of conserving these biogeographic crossroads. Biogeographic crossroads are areas of high species richness and beta diversity, often across many taxonomic groups. They are also regions where representativeness can be achieved with relative efficiency. Recent evidence that ecotones may be loci of evolution suggests that evolutionary processes such as speciation and coevolution may be conserved at biogeographic crossroads. Biogeographic crossroads appear to be areas of high conservation priority and opportunity in both the short and long term and require increased attention in the process of setting conservation priorities. Resumen: Las amenazas a la biodiversidad rebasan los recursos de la comunidad conservacionista y requieren de una cuidadosa priorización de las acciones de conservación. Sugiero que enfocar en las regiones donde intersectan ensambles biogeográficos,"intersecciones biogeográficas", es una estrategia que puede lograr una economía significativa de los esfuerzos de conservación al atender áreas que satisfacen muchos criterios de conservación. Utilicé una combinación de datos de escarabajos Scarabaeine de Bolivia y de otros taxones y localidades de la literatura para considerar los beneficios a corto y largo plazo de conservar estas intersecciones biogeográficas. Las intersecciones biogeográficas son áreas de alta riqueza de especies y de diversidad beta, y probablemente éste sea el caso de muchos grupos taxonómicos. También son regiones en las que se puede alcanzar representatividad con relativa eficiencia. Evidencia reciente de que los ecotonos pueden ser sitios de evolución sugiere que los procesos evolutivos tales como la especiación y coevolución pueden ser conservados en intersecciones biogeográficas. Las intersecciones biogeográficas parecen ser áreas de alta prioridad y oportunidad de conservación tanto a corto como a largo plazo y requieren mayor atención en el proceso de definición de prioridades de conservación. [source] A latitudinal gradient of beta diversity for exotic vascular plant species in North AmericaDIVERSITY AND DISTRIBUTIONS, Issue 3 2008Hong Qian ABSTRACT Determining relationships between the ranges of introduced species and geographical and environmental factors is an important step in understanding the mechanisms and processes of the spread of introduced species. In this study, I examined the beta diversity and latitude relationship for all naturalized exotic species of vascular plants in North America at a continental scale. Beta diversity was calculated as the absolute value of the slope of the relationship between the natural logarithm of the Simpson index of similarity (lnS) and spatial distance between pairs of state-level exotic floras within four latitudinal zones examined. Relative contributions of spatial distance and environmental difference to species turnover between exotic floras were examined. I found that beta diversity decreased monotonically from low to high latitudes: beta diversity for the southernmost zone was shallower than that for the northernmost zone by a factor of 2.6. Regression models of lnS in relation to spatial distance and environmental (climatic and topographical) difference for each latitudinal zone demonstrated that the explanatory power of these variables diminishes monotonically with latitude: the explained variance in lnS is 70.4%, 62.1%, 53.9%, and 33.9%, respectively, for the four latitudinal zones from south to north. For the southernmost zone, 58.3% of the variance in lnS is explained by climate variables and topography, and spatial distance explains only 2.3% of the variance. In contrast, for the northernmost zone, more than half the amount (22.5%) of the explained variance in lnS is attributable to spatial distance, and the remaining (18.9%) of the explained variance is attributable to climate variables and topography. [source] Using generalized dissimilarity modelling to analyse and predict patterns of beta diversity in regional biodiversity assessmentDIVERSITY AND DISTRIBUTIONS, Issue 3 2007Simon Ferrier ABSTRACT Generalized dissimilarity modelling (GDM) is a statistical technique for analysing and predicting spatial patterns of turnover in community composition (beta diversity) across large regions. The approach is an extension of matrix regression, designed specifically to accommodate two types of nonlinearity commonly encountered in large-scaled ecological data sets: (1) the curvilinear relationship between increasing ecological distance, and observed compositional dissimilarity, between sites; and (2) the variation in the rate of compositional turnover at different positions along environmental gradients. GDM can be further adapted to accommodate special types of biological and environmental data including, for example, information on phylogenetic relationships between species and information on barriers to dispersal between geographical locations. The approach can be applied to a wide range of assessment activities including visualization of spatial patterns in community composition, constrained environmental classification, distributional modelling of species or community types, survey gap analysis, conservation assessment, and climate-change impact assessment. [source] Biodiverse, a tool for the spatial analysis of biological and related diversityECOGRAPHY, Issue 4 2010Shawn W. Laffan Biodiverse is a tool for the spatial analysis of diversity using indices based on taxonomic, phylogenetic and matrix (e.g. genetic dissimilarity) relationships. The explosion in georeferenced biological specimen and survey data means there is an increasing need for such tools. Biodiverse supports four processes: 1) linked visualisation of data distributions in geographic, taxonomic, phylogenetic and matrix spaces; 2) spatial moving window analyses including richness, endemism, phylogenetic diversity and beta diversity; 3) spatially constrained agglomerative cluster analyses; and 4) randomisations for hypothesis testing. Biodiverse is open-source and supports user developed extensions. It can be used both through a graphical user interface and scripts. Biodiverse can be downloaded from Assessing the relationship between forest types and canopy tree beta diversity in AmazoniaECOGRAPHY, Issue 4 2010Thaise Emilio Planning of conservation priorities has often taken mapped forest types as surrogates for biological complementarity. In the Brazilian Amazon, these exercises have given equal weight to each forest type as if they were all equally distinct. Here, we examine floristic similarity between forest types to assess the reliability of vegetation maps as a surrogate for canopy tree-community composition. We analyzed floristic differences at the genus level between twelve Amazonian forest types using 1184 one-hectare inventories of large trees with three complementary approaches. First, we compared a map of floristic composition, from a uni-dimensional NMDS ordination of the inventories, with a map of coarser-level forest types commonly recognized as distinct by classification systems across Amazonia. Using Mantel and means-difference tests, we next examined the distance-decay of floristic similarity for all paired samples and for the pairs drawn from within and between twelve more finely divided forest types. Finally, we examined the degree of floristic separation of each pair of the twelve forest types using non-parametric analysis of variance. Maps of floristic composition and coarse-level forest types were highly congruent. At the finer level of classification, similarity was only slightly higher when pairs were drawn from the same versus from different forest types. This was true for all geographic distances. Nonetheless, eighty percent of the 66 paired combinations of forest types were significantly different in the unreduced genus-space and nearly half showed little or no overlap in a two-dimensional ordination. Three types were most distinct from all others: white sand, seasonally dry, and bamboo-dominated forests. Here, we show that forest types exhibit variable degrees of separation. For this reason, treating all fine-level forest types as equally distinct results in poor representation of canopy tree beta diversity. We recommend explicitly considering the degree of floristic separation between all forest types , as presented here for Amazonian flora , as a way to improve the use of this biodiversity surrogate. [source] A diversity of beta diversities: straightening up a concept gone awry.ECOGRAPHY, Issue 1 2010Part 1. The term beta diversity has been used to refer to a wide variety of phenomena. Although all of these encompass some kind of compositional heterogeneity between places, many are not related to each other in any predictable way. The present two-part review aims to put the different phenomena that have been called a beta component of diversity into a common conceptual framework, and to explain what each of them measures. In this first part, the focus is on defining beta diversity. This involves deciding what diversity is and how the observed total or gamma diversity (,) is partitioned into alpha (,) and beta (,) components. Several different definitions of "beta diversity" that result from these decisions have been used in the ecological literature. True beta diversity is obtained when the total effective number of species in a dataset (true gamma diversity,) is multiplicatively partitioned into the effective number of species per compositionally distinct virtual sampling unit (true alpha diversity,d) and the effective number of such compositional units (,Md=,/,d). All true diversities quantify the effective number of types of entities. Because the other variants of "beta diversity" that have been used by ecologists quantify other phenomena, an alternative nomenclature is proposed here for the seven most popular beta components: regional-to-local diversity ratio, two-way diversity ratio, absolute effective species turnover (=regional diversity excess), Whittaker's effective species turnover, proportional effective species turnover, regional entropy excess and regional variance excess. In the second part of the review, the focus will be on how to quantify these phenomena in practice. This involves deciding how the sampling units that contribute to total diversity are selected, and whether the entity that is quantified is all of "beta diversity", a specific part of "beta diversity", the rate of change in "beta diversity" in relation to a given external factor, or something else. [source] Beta diversity and latitude in North American mammals: testing the hypothesis of covariationECOGRAPHY, Issue 5 2004Pilar Rodríguez Several hypotheses attempt to explain the latitudinal gradient of species diversity, but some basic aspects of the pattern remain insufficiently explored, including the effect of scales and the role of beta diversity. To explore such components of the latitudinal gradient, we tested the hypothesis of covariation, which states that the gradient of species diversity should show the same pattern regardless of the scale of analysis. The hypothesis implies that there should be no gradients of beta diversity, of regional range size within regions, and of the slope of the species-area curve. For the fauna of North American mammals, we found contrasting results for bats and non-volant species. We could reject the hypothesis of covariation for non-volant mammals, for which the number of species increases towards lower latitudes, but at different rates depending on the scale. Also, for this group, beta diversity is higher at lower latitudes, the regional range size within regions is smaller at lower latitudes, and z, the slope of the species-area relationship is higher at lower latitudes. Contrarily bats did not show significant deviations from the predictions of the hypothesis of covariation: at two different scales, species richness shows similar trends of increase at lower latitudes, and no gradient can be demonstrated for beta diversity, for regional range size, or for the slopes of the species-area curve. Our results show that the higher diversity of non-volant mammals in tropical areas of North America is a consequence of the increase in beta diversity and not of higher diversity at smaller scales. In contrast, the diversity of bats at both scales is higher at lower latitudes. These contrasting patterns suggest different causes for the latitudinal gradient of species diversity in the two groups that are ultimately determined by differences in the patterns of geographic distribution of the species. [source] Latitudinal gradients in diversity: real patterns and random modelsECOGRAPHY, Issue 3 2001Patricia Koleff Mid-domain models have been argued to provide a default explanation for the best known spatial pattern in biodiversity, namely the latitudinal gradient in species richness. These models assume no environmental gradients, but merely a random latitudinal association between the size and placement of the geographic ranges of species. A mid-domain peak in richness is generated because when the latitudinal extents of species in a given taxonomic group are bounded to north and south, perhaps by a physical constraint such as a continental edge or perhaps by a climatic constraint such as a critical temperature or precipitation threshold, then the number of ways in which ranges can be distributed changes systematically between the bounds. In addition, such models make predictions about latitudinal variation in the latitudinal extents of the distributions of species, and in beta diversity (the spatial turnover in species identities). Here we test how well five mid-domain models predict observed latitudinal patterns of species richness, latitudinal extent and beta diversity in two groups of birds, parrots and woodpeckers, across the New World. Whilst both groups exhibit clear gradients in richness and beta diversity and the general trend in species richness is acceptably predicted (but not accurately, unless substantial empirical information is assumed), the fit of these models is uniformly poor for beta diversity and latitudinal range extent. This suggests either that, at least for these data, as presently formulated mid-domain models are too simplistic, or that in practice the mid-domain effect is not significant in determining geographical variation in diversity. [source] Structure and vertical stratification of plant galler,parasitoid food webs in two tropical forestsECOLOGICAL ENTOMOLOGY, Issue 3 2009MIGUEL R. PANIAGUA Abstract 1.,Networks of feeding interactions among insect herbivores and natural enemies such as parasitoids, describe the structure of these assemblages and may be critically linked to their dynamics and stability. The present paper describes the first quantitative study of parasitoids associated with gall-inducing insect assemblages in the tropics, and the first investigation of vertical stratification in quantitative food web structure. 2.,Galls and associated parasitoids were sampled in the understorey and canopy of Parque Natural Metropolitano in the Pacific forest, and in the understorey of San Lorenzo Protected Area in the Caribbean forest of Panama. Quantitative host,parasitoid food webs were constructed for each assemblage, including 34 gall maker species, 28 host plants, and 57 parasitoid species. 3.,Species richness was higher in the understorey for parasitoids, but higher in the canopy for gall makers. There was an almost complete turnover in gall maker and parasitoid assemblage composition between strata, and the few parasitoid species shared between strata were associated with the same host species. 4.,Most parasitoid species were host specific, and the few polyphagous parasitoid species were restricted to the understorey. 5.,These results suggest that, in contrast to better-studied leaf miner,parasitoid assemblages, the influence of apparent competition mediated by shared parasitoids as a structuring factor is likely to be minimal in the understorey and practically absent in the canopy, increasing the potential for coexistence of parasitoid species. 6.,High parasitoid beta diversity and high host specificity, particularly in the poorly studied canopy, indicate that tropical forests may be even more species rich in hymenopteran parasitoids than previously suspected. [source] Phylogenetic beta diversity: linking ecological and evolutionary processes across space in timeECOLOGY LETTERS, Issue 12 2008Catherine H. Graham Abstract A key challenge in ecological research is to integrate data from different scales to evaluate the ecological and evolutionary mechanisms that influence current patterns of biological diversity. We build on recent attempts to incorporate phylogenetic information into traditional diversity analyses and on existing research on beta diversity and phylogenetic community ecology. Phylogenetic beta diversity (phylobetadiversity) measures the phylogenetic distance among communities and as such allows us to connect local processes, such as biotic interactions and environmental filtering, with more regional processes including trait evolution and speciation. When combined with traditional measures of beta diversity, environmental gradient analyses or ecological niche modelling, phylobetadiversity can provide significant and novel insights into the mechanisms underlying current patterns of biological diversity. [source] Four ways towards tropical herbivore megadiversityECOLOGY LETTERS, Issue 4 2008Thomas M. Lewinsohn Abstract Most multicellular species alive are tropical arthropods associated with plants. Hence, the host-specificity of these species, and their diversity at different scales, are keys to understanding the assembly structure of global biodiversity. We present a comprehensive scheme in which tropical herbivore megadiversity can be partitioned into the following components: (A) more host plant species per se, (B) more arthropod species per plant species, (C) higher host specificity of herbivores, or (D) higher species turnover (beta diversity) in the tropics than in the temperate zone. We scrutinize recent studies addressing each component and identify methodological differences among them. We find substantial support for the importance of component A, more tropical host species. A meta-analysis of published results reveals intermediate to high correlations between plant and herbivore diversity, accounting for up to 60% of the variation in insect species richness. Support for other factors is mixed, with studies too scarce and approaches too uneven to allow for quantitative summaries. More research on individual components is unlikely to resolve their relative contribution to overall herbivore diversity. Instead, we call for the adoption of more coherent methods that avoid pitfalls for larger-scale comparisons, for studies assessing different components together rather than singly, and for studies that investigate herbivore beta-diversity (component D) in a more comprehensive perspective. [source] A latitudinal gradient in large-scale beta diversity for vascular plants in North AmericaECOLOGY LETTERS, Issue 8 2007Hong Qian Abstract Species turnover, or beta diversity, has been predicted to decrease with increasing latitude, but few studies have tested this relationship. Here, we examined the beta diversity,latitude relationship for vascular plants at a continental scale, based on complete species lists of native vascular plants for entire states or provinces in North America (north of Mexico). We calculated beta diversity as the slope of the relationship between the natural logarithm of the Jaccard index (lnJ,) for families, genera or species, and both geographic distance and climate difference within five latitude zones. We found that beta diversity decreased from south to north; within latitude zones, it decreased from species to genera and families. Geographic and climatic distance explained about the same proportion of the variance in lnJ in zones south of c. 50°N. North of this latitude, nearly all the explained variance in lnJ was attributable to geographic distance. Therefore, decreasing beta diversity from south to north reflects decreasing climate differentiation within more northerly latitude zones, and primarily post-glacial dispersal limitation north of 50°N. [source] Dispersal, spatial scale, and species diversity in a hierarchically structured experimental landscapeECOLOGY LETTERS, Issue 5 2005Marc W. Cadotte Abstract Although there has been growing interest in the effect of dispersal on species diversity, much remains unknown about how dispersal occurring at multiple scales influences diversity. We used an experimental microbial landscape to determine whether dispersal occurring at two different scales , among local communities and among metacommunities , affects diversity differently. At the local scale, dispersal initially had a positive effect and subsequently a neutral effect on diversity, whereas at the metacommunity and landscape scales, dispersal showed a consistently negative effect. The timing in which dispersal affected beta diversity also differed sharply between local communities and metacommunities. These patterns were explained by scale- and time-dependent effects of dispersal in allowing spread of species and in removing spatial refuges from predators. Our results suggest that the relative contribution of opposing mechanisms by which dispersal affects diversity changes considerably over time and space in hierarchical landscapes in which dispersal occurs at multiple scales. [source] Effects of an exotic invasive macrophyte (tropical signalgrass) on native plant community composition, species richness and functional diversityFRESHWATER BIOLOGY, Issue 6 2010THAÍSA SALA MICHELAN Summary 1.,The issue of freshwater species being threatened by invasion has become central in conservation biology because inland waters exhibit the highest species richness per unit area, but apparently have the highest extinctions rates on the planet. 2.,In this article, we evaluated the effects of an exotic, invasive aquatic grass (Urochloa subquadripara, tropical signalgrass) on the diversity and assemblage composition of native macrophytes in four Neotropical water bodies (two reservoirs and two lakes). Species cover was assessed in quadrats, and plant biomass was measured in further quadrats, located in sites where tropical signalgrass dominated (D quadrats) and sites where it was not dominant or entirely absent (ND quadrats). The effects of tropical signalgrass on macrophyte species richness, Shannon diversity and number of macrophyte life forms (a surrogate of functional richness) were assessed through regressions, and composition was assessed with a DCA. The effects of tropical signalgrass biomass on the likelihood of occurrence of specific macrophyte life forms were assessed through logistic regression. 3.,Tropical signalgrass had a negative effect on macrophyte richness and Shannon and functional diversity, and also influenced assemblage composition. Emergent, rooted with floating stems and rooted submersed species were negatively affected by tropical signalgrass, while the occurrence of free-floating species was positively affected. 4.,Our results suggest that competition with emergent species and reduction of underwater radiation, which reduces the number of submersed species, counteract facilitation of free-floating species, contributing to a decrease in plant diversity. In addition, homogenisation of plant assemblages shows that tropical signalgrass reduces the beta diversity in the macrophyte community. 5.,Although our results were obtained at fine spatial scales, they are cause for concern because macrophytes are an important part of freshwater diversity. [source] Spatial scale and the diversity of macroinvertebrates in a Neotropical catchmentFRESHWATER BIOLOGY, Issue 2 2010RAPHAEL LIGEIRO Summary 1.,Lotic ecosystems can be studied on several spatial scales, and usually show high heterogeneity at all of them in terms of biological and environmental characteristics. Understanding and predicting the taxonomic composition of biological communities is challenging and compounded by the problem of scale. Additive diversity partitioning is a tool that can show the diversity that occurs at different scales. 2.,We evaluated the spatial distribution of benthic macroinvertebrates in a tropical headwater catchment (S.E. Brazil) during the dry season and compared alpha and beta diversities at the scales of stream segments, reaches, riffles and microhabitats (substratum types: gravels, stones and leaf litter). We used family richness as our estimate of diversity. Sampling was hierarchical, and included three stream segments, two stream reaches per segment, three riffles per reach, three microhabitats per riffle and three Surber sample units per microhabitat. 3.,Classification analysis of the 53 families found revealed groups formed in terms of stream segment and microhabitat, but not in terms of stream reaches and riffles. Separate partition analyses for each microhabitat showed that litter supported lower alpha diversity (28%) than did stones (36%) or gravel (42%). In all cases, alpha diversity at the microhabitat scale was lower than expected under a null model that assumed no aggregation of the fauna. 4.,Beta diversity among patches of the microhabitats in riffles depended on substratum type. It was lower than expected in litter, similar in stone and higher in gravel. Beta diversities among riffles and among reaches were as expected under the null model. On the other hand, beta diversity observed was higher than expected at the scale of stream segments for all microhabitat types. 5., We conclude that efficient diversity inventories should concentrate sampling in different microhabitats and stream sites. In the present study, sampling restricted to stream segments and substratum types (i.e. excluding riffles and stream reaches) would produce around 75% of all observed families using 17% of the sampling effort employed. This finding indicates that intensive sampling (many riffles and reaches) in few stream segments does not result in efficient assessment of diversity in a region. [source] Seasonal trophic dynamics affect zooplankton community variabilityFRESHWATER BIOLOGY, Issue 11 2009BEATRIX E. BEISNER Summary 1. The degree to which communities are variable may be affected by the ecological conditions to which they are exposed and can affect their propensity to form alternative states. We examined the influence of two common ecological factors, predation and seasonal successional stage, on the variability in community composition of herbivorous pond plankton. In a highly replicated, two factor, mesocosm experiment we determined whether beta diversity was affected by seasonal successional stage of the community (two levels), by fish predation (presence/absence) or by their interaction. 2. Several significant changes were found in the composition of the rotifer, cladoceran and copepod assemblages. Most cladoceran abundances showed sharp declines in the presence of fish, while some rotifers, as well as their assemblage species richness, responded favourably to fish. The copepod assemblage was composed of omnivorous and carnivorous species, which added invertebrate predation to the experiment and which intensified as the season progressed. Copepods showed responses to fish predation that depended on seasonal successional stage of the initial community, because of changes in their stage structure and edibility as they grew from nauplii to adults. 3. Community variability was consistently high at the end of each month-long experimental period for both cladoceran and rotifer assemblages, except under two conditions. In the early season treatments, the rotifer assemblages were more consistent (lower beta diversity) in the presence of fish. This was attributed to high population growth rates for rotifers under these ecological conditions because of reduced copepod predation on them through a trophic cascade from fish. Low community variability was also observed in the late season for rotifers when fish were excluded and, as a result, they were exposed to high invertebrate predation from cyclopoid copepods. 4. Results from the early season support theoretical predictions that when community size increases, variability in composition should decline because of an increase in competitive processes over stochastic ones. Late season results suggest that a second mechanism, specialist predation, can also reduce prey community variability. Our study demonstrates that plankton communities may be more predictable under certain trophic web configurations and challenges ecologists to find ways to incorporate such inherent variability into experiments and community theory. [source]
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